Induced pluripotent and multipotent stem cells have the potential to revolutionize various therapeutic applications, especially in the fields of regenerative medicine and pharmaceutical development. One of the obstacles for stem cell-based therapy is the requirement of large number of cells, which can be met by expanding stem cells in a large scale. A number of technical hurdles remain for expansion of such cells using currently available substrates for cell culture using a bioreactor.
Bioreactors have long been practiced as the preferred scale-up method for cell culture. The use of microcarriers for culturing adherent cells is common in industrial practice, such as in bioprocessing. Typical bioreactor vessels employ some means of agitation, such as internal impellers, rocking or shaking mechanisms to suspend the cells and allow mass transfer of nutrients, oxygen and metabolic waste products. The agitation can subject cells to high degrees of flow-induced stress that can damage cells or alter the cell phenotype, especially sensitive ones such as stem cells. A carrier that protects stem cells from agitation-induced damage and provides better stem cell recovery has recently been developed. One of the biggest remaining technological needs is control over stem cell differentiation, both in terms of suppressing spontaneous differentiation as well as enhancing directed differentiation.
Stem cells are inherently susceptible to differentiation based on their local environment, which typically generates the appropriate cell types for the current stage of development or produces cells for generating particular tissues. To control differentiation, the major focus has been on biochemical cues for stem cell growth and differentiation, leading to a great variety of specialized media and surface treatments for the maintenance of stem cell pluripotency or induction of differentiation. Originally, many induced pluripotent stem cells are grown in a co-culture with mouse embryonic feeder cells (MEF) which conditioned the environment to support induced pluripotent growth, however this leads to the potential for xeno-contamination and adds to the inherent biological variability of the system. To avoid contamination, a combination of surface treatments with extracellular matrix proteins, different media formulations or other surface-modifiers have been employed to achieve similar results, though the surface coating of extracellular matrix proteins remains a biologically variable source of growth signals for non-recombinant protein mixtures.
Therefore, cell carriers, which provide protection from flow induced stress and easy separation of the carriers from cells, are an unmet need in the art. The development of cell carriers that facilitates stem cell attachment, proliferation and release, while maintaining stem cell pluripotency or directing differentiation under reduced shear forces is highly desired.